Current lead-in for discharge chambers



Oct. 19, 1965 H. RORDORF' 3,213,182

CURRENT LEAD-IN FOR DISCHARGE CHAMBERS Filed March 27, 1962 2Sheets-Sheet l //v VEN TOR Haas?" fio/woxa ,4 TTORNE V5 Oct. 19, 1965 H.RORDORF 3,213,182

CURRENT LEAD-IN FOR DISCHARGE CHAMBERS Filed March 2'7, 1962 2Sheets-Sheet 2 Fig.2

7 [III vwmvme Hovsr AopaoeF United States Patent M CURRENT LEAD-IN FORDISCHARGE CHAMBERS Horst Rordort, lfangstrasse 17, Weiningen, Zurich,Switzerland Filed Mar. 27, 1962, Ser. No. 182,815

Claims priority, application Switzerland, Mar. 30, 1961,

3,807/61 8 Claims. (Cl. 174-48) The present invention relates to currentlead-ins for discharge chambers designed for the performance ofchemical, metallurgical or other technical processes under the action ofelectrical discharges in gas particularly glow discharges, in which gasis continuously passed through the chamber during the process.

The arrangement of current lead-ins extending into and insulated fromdischarge chambers entails difficulties because the insulating materialmay be destroyed after a short period of operation within the dischargechamber at the points of contact between energized metal parts andinsulating members due to the attack by electrical discharges,particularly where discharge energy is high. Such damage may cause theinsulating members involved to become useless and result in breakdowns.By way of example, if the lead-in to the electrode carrying the cathodicpotential in a glow discharge chamber is covered by a glow seamextending as far as the insulator, the latter will be destroyed by theglow discharge at the junction point between the electrode lead-in andthe insulator where the intensity of the glow discharge is high.

In order to avoid destructions of this kind, the occurrence ofelectrical discharges at the points of contact between energized metalparts and insulating members must be prevented. To this end, variousarrangements and processes have been devised. One of the most commonmeasures comprises the provision of protective gaps delimited bymetallic walls which are located between the discharge chamber and theinsulating material designed to insulate the energized members, thewidth of such gaps being so reduced that an electron released at thewall of the protective gap which carries the cathodic potential cannot,on its path to the wall of the protective gap carrying the anodicpotential, produce so many ions as are on an average required to releasea new electron at the wall carrying the cathodic potential. Where thegap width is so dimensioned, the number of electrons produced at thewall carrying the cathodic potential cannot increase so that noindependent discharge will be set up within this protective gap.Provision of such protective gaps between the discharge space and thepoint of contact between metal and insulating material therefore enablesthe harmful action of electrical discharges on the insulating materialto be avoided.

These protective gaps have in practice been found to be effective wherethe operating pressure in the discharge chamber is comparatively low.Above an upper pressure limit p =c.,\ /d which, with a meanproportionality constant c, is proportional to the relationship A /d ofthe mean free length of path A of the gas under hormal pressure presentin the discharge chamber to the gap width d, these protective gapshowever become ineffective. This may be explained by the fact that thenumber of ions which may, on an average, be produced by an electron perunit path is inversely proportional to the mean free length of path ofthe electron involved and, accordingly, proportional to the pressure.When the upper pressure limit is reached, the average number of ionsproduced by an electron on its way through the gap has increasedsufficiently to enable a new electron to be released so that anindependent discharge can be maintained. With a predetermined type ofgas and therefore k predetermined, this upper pressure limit, as may beseen from the above equation, can be 3,2l3,182 Patented Oct. 19, 1965increased only by reducing the gap width. The eifectiveness of the gapwidth is therefore limited in the upward direction relative to thepressure existing in the discharge chamber because the gap Width cannotbe reduced at will, for purely mechanical reasons. It has therefore beenproposed to design the protective gap, which was previously known onlyin the form of a cylindrical gap, as a fiat gap in order, amongst otherthings, to making a further reduction of the gap width possible. Thisenabled the upper pressure limit to be quite substantially raised to alevel normally entirely sufficient.

In order, however, to become entirely independent of this upper pressurelimit, new means independent of this interrelationship had to be sought.The problem underlying the present invention was therefore to provide acurrent lead-in in which the protection of the insulating materialagainst the attack by electrical discharges is ensured independently ofan upper limiting pressure.

The solution of this problem was achieved for current lead-ins with anenergized inner lead and an insulator provided for its insulation, fordischarge chambers designed for the performance of such chemical,metallurgical or other technical processes under the action ofelectrical gas discharges, and particularly glow discharges, in whichgas is continuously passed during the process. The present inventionprovides such a current lead-in with means designed to form, between thejunction points between metal and insulator which are subjected to theattack by discharges on the one hand and the discharge chamber on theother, a zone comprising at least a portion of the gas flowing throughsaid chamber, the said zone possessing a pressure so much higher thanthe mean pressure in the discharge chamber that no glow discharge can beset up within the zone.

This is achieved preferably by means designed to inhibit the efliux ofgas from the zone of higher pressure into the discharge space within thechamber. These means inhibiting the gas efiiux may advantageously be sodimensioned that the gas is held up and so that the zone of higherpressure is formed at least largely by dynamic pressure.

The means inhibiting the gas efliux may advantageously be so adjustablethat the flow resistance formed thereby may be varied.

In order to supply the gas, the inner lead is preferably designed, inthe portion of its length. which passes through the wall of the chamber,as a gas inlet provided with one or more orifices so arranged that thezone of higher pressure is produced, when gas is flowing, at a point ofdischarge between the inner lead and insulator but within the dischargechamber.

A current lead-in with an insulator enclosing the inner lead may, by wayof example, advantageously be designed so that the gas supply line opensinto an annular space enclosing the inner lead, the said space beingdelimited by the inner lead, the end of the insulator and a metal jacketembracing part of the length of the insulator, and within which spacethe zone of higher pressure is formed when gas is flowing. This annularspace is preferably delimited, in the direction toward the dischargechamber, by a ring connected with the inner lead, the said ring being sodimensioned and arranged that only a narrow annular gap remains open forthe escape of the gas between the ring and the metal jacket. The metaljacket embracing the insulator should preferably be arranged so that ithas no electrical potential thereon.

Two embodiments of the present invention are described in greater detailin conjunction with the drawings in which:

FIG. 1 shows a current lead-in according to this invention in which thezone of higher pressure is obtained, by dynamic pressure, in a space ofrestricted cross-section which has an opening communicating with thedischarge chamber,

FIG. 2 shows a current lead-in according to this invention in which thezone or higher pressure is formed by the configuration of the gasstream, and

FIGS. 2a, 2b and 2c illustrate structural details of difierent forms ofthe invention.

In principle, the operation of the invention is based on the fact that acertain voltage is required to maintain, e.g., a glow discharge at agiven gas pressure. The level of this voltage is essentially dependenton the gas pressure existing in the discharge chamber, but is entirelyindependent of the voltage in the range of the normal cathode drop andonly slightly dependent thereon in the area of high-energy glowdischarges. At a certain mean pressure present in the discharge chamberand with a corresponding voltage which produces a glow discharge in thedischarge chamber, it is therefore possible to prevent the formation ofa glow discharge in any desired zone by locally increasing the gaspressure. In discharge chambers designed for the performance of suchprocesses in which gas is continuously passed through the chamber, thegas stream itself may advantageously be employed to obtain such a localpressure increase, by forming a dynamic pressure zone through which thegas must flow.

By way of example, the embodiment of a current lead-in according to thisinvention is based on this principle of forming a dynamic pressure zone.In FIG. 1 an inner lead 1 carrying a cathodic potential is attached tothe outside of the wall 5 of the discharge chamber by means of theinsulating sealing plates 2 and 3 and the clamping plate 4, andinsulated from the chamber wall 5 by means of the insulating tube 6. Thegas to be passed through the chamber is supplied to the said chamber viathe bore '7 provided in the inner lead. Through the orifices of this gassupply line, the gas will flow into the annular zone 9 which enclosesthe inner lead, the said zone 9 being delimited, apart from the innerlead, by the insulating tube 6, a metal jacket it? and a ring 11 carriedby the inner lead. The metal jacket 10 embraces the insulator 6 on theportion of its length which projects into the interior of the chamberand is attached to the inside of the chamber wall 5 by means of theinsulating sealing plates 14 and 15.

The gas present in the annular zone 9 can emerge only through the narrowannular gap 12 between the ring 11 and the metal jacket lid, in whichgap high flow resistance inhibits the free efilux of the gas.Accordingly, the gas flowing into the zone 9 through the orifices 8 willbe restrained in this zone. The dynamic pressure thus built up in thezone 9 is higher by the pressure drop at the flow resistance of the gap12 than the pressure in the interior 13 of the chamber.

If the quantity of gas passed is predetermined according to the volumesup-plied per unit time, the dynamic pressure in the zone 9 isproportional to the pressure in the discharge chamber independently ofthe absolute pressure value, the said ratio being determined by theproduct of the flow resistance of the gap 12 and the gas volume suppliedper unit time. If the gas volume passed is determined according to theweight supplied per unit time, the pressure drop at the flow resistanceof the gap 12 and the pressure difference between the dynamic pressurein the zone 9 and the pressure in the discharge chamber are constantindependently of the absolute value of the pressure.

In general, any desired values can be set for the dynamic pressure andthe pressure in the discharge chamber while the amount of gas passed isoptional. By way of example, the pressure in the discharge chamber maybe kept constant by an appropriate pump arrangement while the desiredlevel of the dynamic pressure in the zone 9 can be adjusted byappropriately setting the pressure of the gas supplied.

The fiow resistance of the gap 12 is advantageously so adjusted that thedynamic pressure in the zone 9, independently of whether the gas passedis determined according to the volume supplied or the weight per unittime, is at all events sufliciently high relative to the pressure in thedischarge chamber to prevent the formation of a glow discharge in thezone 9. The level of flow resistance in the gap I2 may, e.g., be changedby modifying the cross-section and, respectively, the width of the gap12. In certain applications it may be of advantage to provide thecurrent lead-ins with means for altering the width of the gap I2 andthereby the flow resistance therethrough particularly if the dischargechamber for which the current lead-ins are designed is to be employed incontinuously varying operating conditions or if it is designed for usein a laboratory for the performance of a variety of processes.

If the current lead-in is designed for an operation in which thequantity of gas passed is determined independently of the absolutepressure value, and by the volume supplied per unit time; the flowresistance may be smaller than in cases where operating conditions varybecause the ratio between the dynamic pressure and the pressure in thedischarge chamber remains constant. By way of example, in manyapplications a dynamic pressure/discharge chamber pressure of 2:1 willsufiice to prevent the occurrence of a glow discharge in the dynamicpressure zone. The constancy of this ratio, however, will be maintainedonly while the flow resistance may be regarded as being substantiallylinear, i.e. while the pressure drop at the flow resistance is causedmainly by the friction of the gas molecules on the fixed walls formingthe flow resistance so that it is approximately propor tional to thenumber of the gas molecules passing the flow resistance.

In designing the current lead-in it should further be ensured that theflow resistance of the gas supply line to the dynamic pressure zone,i.e. the bore 7 in FIG. 1, is as low as possible relative to the flowresistance in gap 12.

In the determination of the flow resistance in gap 12, account should betaken of the discharge energy to be supplied to the discharge chamber.The flow resistance should be so controlled that the pressure in thedynamic pressure zone will at all times be so much higher than thepressure in the discharge chamber that the highest possible voltage atany possible pressure level in the discharge chamber is insufiicient tocause a glow discharge in the dynamic pressure zone.

Provision of such a high dynamic pressure in the zone 9 ensures that noglow discharge can be produced at the junction point 16 between theinner lead and the insulator, and the insulator is thus protectedagainst the harmful attack by the glow discharge.

FIG. 2 shows a further embodiment of a current leadin according to thisinvention which differs from the current lead-in of FIG. 1 in that thenecessary dynamic pressure in a zone in front of the transition point 17between the inner lead and the insulator is obtained in a manner. Theflow of the gas supplied is here controlled in such a manner that thegas forms, inwardly of the junction point 17, a closed jet cone of jetring I with flow in the radial direction. This causes a pressure to bebuilt up in the annular zone 19 which, owing to the delimitation of thezone 19 by the inner lead 2t the insulator 21 and the metal jacket 22and the fact that the gas can flow out of this zone 19 only through thejet cone 18, is about the same as the pressure existing within the jetcone 18. From the jet cone 18, the pressure rapidly decreases in thedirection of the interior of the chamber 23.

With a current lead-in so arranged, care should be taken that thepressure is kept substantially constant along a circumferential line onthe jet cone, i.e. that the flow should be uniform in all radialdirections. FIGS. 2a,

2b and show means for meeting this requirement. FIG. 2a show show theportion of the inner lead in the region of the jet cone 18 might bedesigned. FIG. 2b shows another possibility and represents a section ofthe inner lead at the point where the jet cone is discharged around theinner lead. The streamlined design of the connecting pieces 24 whichjoin the upper and lower portions of the inner lead prevents zones witha lesser flow density relative to the .ambient zones from being formedbehind the connecting pieces. FIG. 20 in turn reveals a furtherpossibility and is an exterior view of the point of the inner lead wherethe jet cone is formed around the inner lead. The staggered rows ofholes 25 represent the orifices of holes which extend from the gas linelo cated at the centre of the inner lead to the outer surface thereof.The fact that these orifices are staggered enables a closed jet cone tobe formed.

Besides the embodiments shown in FIGS. 1 and 2 there are many otherpossible means for creating zones of higher pressure relative to themean pressure in the discharge chamber and inwardly of the transitionpoints subject to the attack by discharges. The invention is thereforenot limited to the embodiments shown but is to be limited only by thescope of the appended claims.

Having now particularly described and ascertained the nature of my saidinvention and the manner in which it is to be performed, I declare thatwhat I claim is:

1. In apparatus for performing processes in electrical discharges in gascomprising: means defining a wall of a chamber; a current lead-inextending through said wall; insulation between said lead-in and saidWall; means for conducting a continuous stream of gas into and throughsaid chamber; means for directing at least a portion of said stream intoa zone encompassing the junction between said insulation and saidlead-in, in said chamber; means for confining said gas in said zonesuificiently to maintain a gas pressure in said zone higher than thepressure in said chamber whereby to prevent any glow discharge in saidzone.

2. Apparatus as defined in claim 1 wherein means are provided torestrict flow of gas from said zone into said chamber to maintain saidhigher pressure in said zone.

3. Apparatus as defined in claim 2 wherein said lastnamed meanscomprises a flow passage communicating said zone with said chamber, saidflow passage being dimensioned to otter greater resistance to gas flowthan said means for directing said portion into said zone whereby saidhigher pressure is produced by dynamic pressure from said portion.

4. Apparatus as defined in claim 3 wherein the dimensions of said flowpassage may be adjusted whereby to vary the pressure in said zone.

5. Apparatus as defined in claim 1 wherein said means for conductingsaid stream comprises a passageway through said lead-in; and orifices insaid lead-in adjacent said junction, communicating with said passagewayand arranged to direct said gas into said zone.

6. Apparatus as defined in claim 5 wherein said insulation surroundssaid lead-in and has an inner end face; a metal jacket surrounding saidinsulation and extending inwardly of said chamber past said end face, inspaced relation to said lead-in, the annular space bounded by saidlead-in, insulation end face, and extending portion of said jacketcomprising said zone.

'7. Apparatus as defined in claim 6 including an annular ring on saidlead-in, spaced from said end face and extending toward said jacket; theouter periphery of said ring being adjacent but spaced from said jacketto define therewith a narrow annular space constituting said flowpassage.

8. Apparatus as defined in claim 6 wherein said metal jacket isinsulated from any source of electrical voltage whereby it is at zeropotential.

References Cited by the Examiner UNITED STATES PATENTS 2,160,660 5/39Hobart. 2,809,228 10/57 Dutton 17431 2,837,654 6/58 Berghaus et al.204-464 DARRELL L. CLAY, Acting Primary Examiner. JOHN P. WILDMAN, JOHNF. BURNS, Examiners.

1. IN APPARATUS FOR PERFORMING PROCESS IN ELECTRICAL DISCHARGES IN GASCOMPRISING: MEANS DEFINING A WALL OF A CHAMBER; A CURRENT LEAD-INEXTENDING THROUGH SAID WALL; INSULATION BETWEEN SAID LEAD-IN AND AIDWALL; MEANS FOR CONDUCTING A CONTINUOUS STREAM OF GAS INTO AND THROUGHSAID CHAMBER; MEANS FOR DIRECTING AT LEAST A PORTION OF SAID STREAM INTOA ZONE ENCOMPASSING THE JUNCTION BETWEEN SAID INSULATION AND SAIDLEAD-IN, IN SAID CHAMBER; MEANS FOR CONFINING SAID GAS IN SAID ZONESUFFICIENTLY TO MAINTAIN A GAS PRESSURE IN SAID ZONE HIGHER THAN THEPRESSURE IN SAID CHAMBER WHEREBY TO PREVENT ANY GLOW DISCHARGE IN SAIDZONE.